How to plant and grow vibrant dahlias

The brightness of the flowers, complex shapes and rich foliage make dahlias a glorious addition to the garden from mid to late summer. What's more, dwarf types can be used to fill window boxes, pots or edge sunny beds. Here's how to make your dahlias flourish.

Dahlias need full sun and a rich, porous soil that retains moisture well but drains easily.

• Ideal soil pH is neutral to slightly acid.

Locate dahlias in a warm, sunny spot where there is good air circulation.

• A site with some shade from the afternoon sun will do.

Plant tubers as soon as the danger of frost no longer exists – mid to late spring in most areas.

Spacing

• Allow 60 to 90 centimetres (25 to 35 inches) between tubers for one and a half metre (five foot) dahlias, 60 centimetres (25 inches) between for one metre (three foot) plants, and 40 centimetres (15 inches) between for shorter ones.
• New growth comes from eyes at the base of the previous year's stem. Each stem has several tuberous roots. These can be planted as a clump or divided into single tubers.

Planting

1. In the planting bed insert a three-centimetre-square (one-inch-square) stake long enough to support tall plants. In front of it dig a 15-centimetre-deep (six-inch-deep) hole.
2. Prepare a mixture of half peat moss and half soil, and incorporate about a handful of bone meal.
3. Fill the hole with this mixture to a level that will bring the tuber's eye to about five centimetres (two inches) below the surface.
4. Place the tuber in front of the stake with the eye against it. Cover the tuber to ground level with the soil and peat moss mixture.
5. Firm the soil gently over the tuber.

Except in extremely arid regions, do not water until new growth begins. Remember to label the stake.

Dahlia tubers can also be started into growth indoors ahead of time.

• If more plants are needed, divide tubers when the new shoots are about two centimetres (one inch) tall. Harden the plants before planting out.

If you wish to keep your dahlias in a container, they will have to be moved into a larger pot than the one in which they were grown from tubers.

• Their feeding and sunlight requirements are pretty much the same as dahlias planted in the garden.

Young plants in pots can be bought from mail-order growers, local nurseries, garden-supply centres and home improvement centres.

• Mail-order houses generally ship when it is the appropriate time for planting in your area – after the last frost has occurred.

Planting pot-grown dahlias

Pot-grown plants are planted in much the same way as tubers.

1. Before you plant, set out stakes; space according to final size.
2. Water the plants lightly.
3. Prepare a mixture of half soil and half peat moss; work a handful of bone meal thoroughly into the mixture so that it is evenly distributed.
4. Next to the stake dig a hole five to eight centimetres (two to three inches) deeper than the root ball and wide enough to fit it. Add a few handfuls of the mixture.
5. Remove the plant from the pot with soil ball intact. If the roots appear twined, do not try to get them loose.
6. Set the ball in the hole with its top five centimetres (two inches) below soil surface. Make sure the stem is straight and close to the stake.
7. Fill the hole with the soil and peat moss mixture and firm it down, leaving a shallow depression around the stem in which moisture can collect to give plants a good start.

After about two days water well. When the plant begins to show signs of top growth, fill up the depression around the stem with soil, and firm it down level.

• Dahlias are very frost sensitive and a late frost can kill newly set-out plants.
• Be sure to cover dahlias if a frost is forecast. Bottomless soft drink bottles make good mini-greenhouses.

Although care has to be taken in springtime to avoid exposing your dahlias to frost, the reward is a summer-long display of bold, vibrant and showy flowers that add real character to any garden.